It ended in sorrow and frustration, the Celtics outplaying the Heat for the better part of 40 minutes before a certain form of reality set in. The Heat ended a run of six consecutive fourth-quarter lead changes with a devastating run of 18-4, and that was that. Miami will play the young and dynamic Oklahoma City Thunder in the Finals and the Celtics will start working on the rest of their franchise life, one that does not figure to include Allen or Garnett, although, despite all the educated speculation, nothing is written in stone.

“Honestly,’’ said Rivers, “I just thought we had nothing left. You could see it as a coach.

“I was trying to push every button, but we were hitting the front rim, we were starting to throw the ball away, and they were beating us off the dribble. It was a group that did everything we asked of them, but we came up short.’’

The five-year run of the Big Three - we’ll get to Rajon Rondo in a while - began officially on Oct. 6, 2007, with an 89-85 exhibition triumph over Toronto in, of all places, Rome. There were 11,118 on hand at the Palalottomatica, and we will never know just how many of them appreciated what they were seeing.

Their actual NBA debut came on Nov. 2, when they defeated Washington by a resounding score of 103-83. Garnett had 22 points and 20 rebounds. Pierce had 28. Allen had 17. John Henry, Larry Lucchino, Tim Wakefield, Jacoby Ellsbury, Manny Delcarmen, Bob Kraft, Wes Welker, Laurence Maroney, Vince Wilfork, and Junior Seau were among the luminaries who saw the era get off to a nice start.

And now it ends in AmericanAirlines Arena, with the screaming PA announcer, the in-house disc jockey, the quite entertaining band, and all the rest of the hoopla that is there to distract the fans from the basketball, which, when played the way it was in those final eight minutes, is of the highest quality.

The Heat took this game away from the Celtics. They did it with a terrific two-way surge in which they showcased the talents of their own Big Three, led by LeBron James, who played a brilliantly mature, but understated game, finishing with 31 points and 12 rebounds while playing all but the final 28.3 seconds.

“I really thought he played a smart, aggressive game,’’ lauded Rivers. “He let the game come to him, and he took over after that, which is what great players do.’’

Nothing LeBron does will satisfy his harshest critics, but to those who say he always shrinks in the fourth quarter, his 11-point, two-assist closing performance in a game that was tied at 73-73 after three should mute them for a little while.

But he had help, most notably in the person of Chris Bosh, the man mockingly known as the “Ringo’’ of the Heat. Just having him on the floor makes Miami a better team, and when he’s shooting 8 for 10 and dropping in a pair of fourth-quarter threes the Heat aren’t going to do very much losing. If he’s Ringo, then let it be said he knows how to follow Paul and John’s lead.

Asked how the Celtics had managed to contain LeBron to a large degree, Rivers had an answer. “We needed Bosh’s guy to help slow down LeBron, if you want to simplify,’’ Rivers explained. “And Bosh made his shots. He was the X-factor. He was exactly what they needed.’

For 3 1/2 quarters, the Celtics did all any reasonable person could ask. They led after one (27-23) and they led at the half (53-46).

“I’m really proud of the way they played, especially early on,’’ Rivers said. “They had the fight in them, and I could see they were going to play the right way.’’

The only real problem was three early fouls for Garnett, who picked up two offensive, the second of which could politely be called “bogus.’’ Doc claimed it threw Kevin out of rhythm for a long stretch.

But with Brandon Bass throwing in 14 points and Rondo again orchestrating matters (10 first-half assists), the Celtics parlayed a strong, overplaying defense and good ball movement into that halftime advantage.

Rondo would finish with yet another triple-double (22-10-14). “I already thought he was in that [elite] class,’’ Rivers said. “If he’s not, now he is.’’

Rondo’s going to be there for a while. Pierce is destined to be a Celtics lifer. But Allen and Garnett are free agents, and common sense says that suitors will be lining up from the Atlantic to the Pacific to pay one of these guys to be the missing piece of a perceived championship puzzle. If Doc had his way, everyone would be back. But he knows better than anyone else that management has broader, long-range concerns.

So, this is where it almost undoubtedly ends.

In Miami.

With honor.

Bob Ryan is a Globe columnist and host of Globe 10.0 on Boston.com. He can be reached at ryan@globe.com.